The present invention relates to an apparatus for cutting a well casing.
Prior to the present invention, the apparatus used for cutting well strings or casing cutters comprised devices having cutting arms pivotally connected in longitudinal slots in the side of a tubular housing and having a suitable means therein for pivoting the arms outwardly. The upper surface and sometimes the outer end of the arms included material deposited thereon which would cut into casing when the tool is rotated within the casing. Thus, if sufficient force is applied to pivot the arms, they will cut through one or more casings so that they may be recovered as in the case of submarine wells which are being abandoned or to remove damaged casing from a well for replacement with new casing. A typical example of such apparatus is shown in U.S. Pat. No. 3,419,077.
With prior casing cutters, the arms need resurfacing to maintain them in proper condition for cutting. The deposit of the material on the arms is done with heat similar to a welding process and such deposit has a tendency to distort the arms making them unsuitable for reuse, and oftentimes causing cracks on the interface between the face material and the deposit. Resurfacing of the arms in a manner which makes them suitable for reuse is normally done only at a manufacturing facility. This is expensive and time consuming and requires that for each casing cutter, several spare arms be available at the wellhead for quick replacement.
Another disadvantage of the devices of the prior art is that some of them have required that the actuating device engage a surface on the arms to cause them to be urged outwardly. This surface is a cam surface and subject to severe wear in use, and when wear has progressed sufficiently far, the arm no longer would be used or repaired.